Fluid electrical delay line



Nov. 18, 1958 T. H. CHAMBERS 2,851,246

FLUID ELECTRICAL DELAY LINE Filed April 19, 1949 2 Sheets-Sheet 1 INVENTOR. 96 TORRENCE H. CHAMBERS ATTORNEY Nov. 18, 1958 T. H. CHAMBERS 2,861,246

FLUID ELECTRICAL DELAY LINE 2 Sheets-Sheet 2 Filed April 19, 1949 INVENTOR.

TORRENCE H. CHAMBERS mowmwmlzoo -24 HWH mu MAO 303 Q a Q G f w 0 EOE ATTORNEY United States Patent 7 FLUID ELECTRICAL DELAY LINE Torrence H. Chambers, Washington, D. C. Application April 19, 1949, Serial No. 88,471

4 Claims. (Cl. 333-30) (Granted under Title 35, U. S. Code (1952), see. 266) This invention relates in general to delay lines, and more specifically it is an improvement over the delay line disclosed in application Serial No. 688,413, filed August 5, 1946, by I. H. Page.

In particular the invention is concerned with the type of delay line which finds extensive use in moving target radar indicators wherein each echo signal is subjected to a time delay equal to the pulse repetition period of the transmitter.

In general, delay lines used in such systems consist of a compressional wave transmitting medium confined between an electromechanical driver and reproducer. The driver and reproducer are usually piezoelectric crystals, while the transmitting medium is in most cases mercury.

In operation, the electrical signal to be delayed is applied to the driver element causing the same to vibrate, mechanically. .The mechanical vibrations thus produced are in turn propagated as a compressional wave through the transmitting medium to the reproducer element where the delayed mechanical vibrations are reconverted into electrical vibrations. The electrical signal produced at the reproducer is of the same character as that applied to the driver, but is delayed in time by an interval equal to the time required for the compressional wave to travel through the transmitting medium.

While in the past delay lines of the same general character as above described have beenwidely used in the art, experience has shown that the same frequently undergo both momentary and sustained interruptions in their operativeness when the line is subjected to shock or vibration such as encountered in various mobile installations and particularly in installations aboard sea going vessels.

It is accordingly an object of this invention to provide a rugged, reliable, fluid electrical delay line,

It is another object of this invention to provide an improved fluid electrical delay line capable of substantially uninterrupted operation under severe conditions of shock and vibration.

. Other objects and features of the present invention will become apparent upon a careful consideration of the following detailed description when taken together with accompanying drawings; in which:

Fig. 1 is a simplified plan section of one embodiment of the present invention, 1

Fig. 2 isa partially cut away top elevational view show ing in more detail an exemplary embodiment of this invention,

Fig. 3 is a partially cut-away side elevational view of the embodiment shown in Fig. 2, and

Fig. 4 is an enlarged sectional viewof one of the crystalsholders 34 or 36 shown in Fig. l.

In the preferred embodiment of the invention, as illustrated in simplified form in Fig. 1, the delay line is in the 'form of atank, and comprises a flat base plate preferably made of stainless steel or the like. 'The .upperface of the base plate is divided, preferably by milling, into a Ice] plurality of similar longitudinal, liquid containing channels 11 through 15, the sides of which are defined by a plurality of septa 16 through 19 formed in the milling operation. Attached to the side faces of the base plate 10, such as by machine screws 30, is a pair of side plates 20 and 21. Similarly attached to the ends of the base plate 10, again such as by machine screws 31, is a pair of end plates 22 and 23. The side and end plates 2021 and 2223, respectively, are bolted together by screws 31 to provide a rigid tank like structure for holding the liquid filling of the delay line. The side and end plates 20-21 and 2223 are tapped, as shown at 32, at regular intervals along their upper edges to permit the attachment of a top plate (not here illustrated) for the line.

The purpose of dividing the delay tank intoseveral longitudinal channels as is quite apparent from the drawings is to conserve space. That is, by connecting the several channels in folded back relation or in tandem so to speak a comparatively long delay line can be obtained from a relatively short tank. For this reason the adjacent septa abut opposite end walls 22 and 23. In particular alternate septa 16 and 18 are milled to permit intimate contact at their left hand ends with the left hand end wall 23. Their right hand ends, however, are terminated short of, or in spaced relation with the right hand end wall 22. Similarly, septa 17 and '19 are milled to lie in intimate contact at their right hand ends with the right hand wall 22. Their left hand ends,

however, terminate short of, or in spaced relation to the left hand end wall 23.

The line is thus divided into five rectangular crosssectional channels 11 through 15 of equal width, length and depth.

Inserted in the left hand end wall 23, in the upper end thereof as viewed in this figure, is a transmitting crystal only the holder for which, generally designated at 34, is visible in this figure. The transmitting crystal holder 34 extends through the end wall 23 and cornmunicates with the first channel 11 of the line and is secured to end plate 23 by suitable machine screws 33. To provide a liquid seal in the line at the point of entrance of the crystal holder 34 a suitable annular rubber gasket 35 is inserted in the annular space formed by the annular recess 36 cut in the end plate 23 and shoulder 37 formed on the holder 34.

From the foregoing it will be apparent that a compressional wave produced by vibration of the transmitting crystal 34 will travel to the right, as viewed in Fig. 1, through the mercury in channel 11. In order to reflect the wave-back and along the next adjacent channel 12, a right angle corner reflector 39 is provided and as illustrated in this figure is so mounted, as by machine screws 39A that its apex is aligned with the septa 16. The right angle facing on this corner reflector extend respectively to septa 17 and side plate 20. Similar reflectors, typified at 38 are used to join channels 12 and 13, 13 and 14, and 14 and 15 in folded relation. Thus a compressional wave originating at the transmitting crystal is reflected in succes'sionfirst to the left and then to the rightlsuccessively through the several channels 11 through 15 until it reaches the receiver crystal 36.

The receiving crystal 36 is mounted on the right hand end wall 22 and communicates with the last channel 15 in the same manner as the transmitting crystal 34. The electrical signal reproduced at the receiving crystal'is of the same character as that applied to the tions in 'which little or no shock or vibration is encountered; it is wholly unreliable for ship board use. I have found the inadequacy of the line results from a tendency of the mercury to pull-away from intimate contact with the crystals whenrthe line ;is; subjectedlo shock'and vibration. This effect results inbothmornentar y and sustained interruptions in the operations ,of the line.

As previously noted it is a major object ,of thisinvem tion to provide a line capable of substantially continuous operation under severe conditions of shock and vibration. To this end I have constructed a delay line as better illustrated in Figs. 2 and. 3 wherein the .mercury or liquid filling of the line is held in'the line under.pressure. Referring now to Figs. 2 and,3, it will be observed that this pressurized feature is accomplishedthrough the use-of a stand-pipe 50 having a metallic piston 51- movable therein.

- The stand-pipe 50 is preferably made of rectangular stock ,bolted or otherwise secured to the top plate 52 covering the line and contains an axial cylindrical bore 53 in which the piston 51 rides. The stand-pipe communicates with the cavity or channels comprising the line through a pair of registering bores 54 and 55 formed in the stand pipe 50 and the top plate 52 respectively, The junction of the bores 54 and 55. is lined with a metallic tubular insert 56 which carries a flange 57 adapted to snuggly fit into adjacent circular recesses 58 and 59 formed in the abutting faces of the stand-pipe and top cover plate of the line. A pair of circular rubber gaskets 60 and 61 are fitted into the recesses 58 and 59 on opposite sides of the flange 57 to provide a liquid tight. seal .at the junction. The insert 56 is preferably made with a small internal diameter operativeto prevent vibrational resonance occurring in the stand-pipe 50 from being transmitted to the mercury in the main delay tank.

In other words the small bore in the insert 56 functions to mechanically decouple the mercury in stand-pipe 50 from that in the delay line tank.

' A plate 62 is provided to cover a filling port 63 formed in the stand-pipe over the registering bores 54 and 55. Plate 62 is bolted to the stand-pipe and is provided with a.cylindrical raised portion 64 adapted to snuggly fit into the filler bore 63. A suitable circular rubber gasket 65 is provided to effect a liquid seal for the filler plate.

In filling the line with mercury, plate 62 is removed and the line comprising the several channels 11 through :15, and the portion of the stand-pipe to the right of the piston 51 is completely filled with mercury. The plate 62 is then bolted back in place and air'pressure is applied tothe air inlet 66 to urge the piston to the right thereby compressing the mercury in theline.

The use of air pressure for purposes ofpressurizing the line is only exemplary and other means for urging thepiston to the right can be employed. For'example a compression spring inserted between-piston 51 and'end' plate 66A of the stand-pipe 50 could'be used if desired. In any event best operation of the line can be secured under pressure of 35 pounds per'square inch or more depending upon the degree of shock'and vibration to which the line is subjected and upon the effective height of the head of mercury or length of the line.

Interruption or failure in the operation of a liquid delay line in addition to that caused by ordinary shock and vibration can also arise in response to a sharp blow dealt to the line itself'such as, by. tapping the'samewith afslcrew-driver. This is, known as the .screw-driver effect and is believed to cause failure of the line by. fbrmation of minute bubbles of air in the mercury. Thesebubbles are possibly formed'by the rare fraction ofithemercury due to the sonic wave travelling out from the-point of impact causing air dissolved in the mercury to be released.

To avoid this difiiculty the line may be firstevacuated andthen-filled with mercury, or alternatively out .gas sed i ribs 72 and 73 formed in the face of the corresponding end plate22or 23. "For similar reasons the side plates may be,provided..wit h longitudinal recesses, asshown in Fig. 2, 74 and 75 formed therein while the top cover plate can be provided with mating ribs.

For shock mounting, the crystal holders, typified at 36, in Fig. 2, are provided with a rubber washer as shown at interposed-between'the end wall'of the tank and crystal holder flange.

To provide a liquid seal for the crystal holders a second rubber gasket 81 is inserted between the shoulder 82ofthe crystal holder and the recess 83 formed in the end wall of "the line;

For convenience in replacement thecrystal and crystal mount are made as a single integral unit as illustrated in cross section in Fig. 4 towhich reference-is now made. The crystal holder'as herein illustrated comprises an outer generally tubular-shell having a mounting =flange 91- integrally formed on the outside thereof. -Shell-90- is internally bored with a large diameter adjacent -the mounting endthereof and a smaller diameter at the open end thereof. -The cr-ystalmount comprises an outer metallic" shell-':92, an insul-ating insert 93 press fitted thereinand finally'a crystal elect-rode 94- press-fitted into the insulating insert-93. Electrode 94 is terminated'in a disc-like'plate 95 at one end thereof and a threaded-section 96 on the other end thereof. The threaded end is provided for the purpose ofmaking a wired input or output connection to the crystal. A-iiat piezoelectriccrystal- 97 is cemented to the disc end of the electrode 94 and extends over the edges thereof as shown in the-'fiigure.

In assembly, the crystal, the electrode 94, the insulating insert 93 and the retaining shell 92 are all mounted as a unit. rubber sealinggasket 98 and metallic retaining ring 99 are inserted within the outer shell 90 as shown. The metal retaining ring'99 is formed with'two diameters as shownto provide a shoulder thereon whereby pressure-within the-dine-forces the ring 99 down' tighter against the gasket 98 providing a better seal undet-pressure.

'To provide shocK mounting, the retaining shell 92 is recessed asshown at ltloto perm'it receipt of a-circular rubb'er'gasket'101. A cover plate 102 is provided with a mating circular head adapted to fit into the recess-100 and completely confine the gasket 101. Plate'1 02 is bolted to outer shell 90 to permit easy-removal-of'the crystal cartridge and -thereby easy replacement of the same;

While I haVe shown-anddescribed only certain' and specific embodiments of the present invention, it must be understood that 1' am fully aware of the many modifications possible thereof; Therefore this invention is not to be limitedexcept as-herein indicated by the-scope ofthe disclosure.

The invention described herein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof any-roya-lties thereon or therefor.

What is claimed is:

- l In a" delay 'line, a -'first'g as-tight container, a'nilectrical driving element-mounted in said first gas-tight-com tainer, an electrical reproducer mounted in-said first gastight container in spaced relation to said *driving element, a po'rtin saidifirst gas-.tightscontainer, asecond gas-tight container. connected ;to ,said port forming .a gas-tighhcounectio'n, saidisecond gas-tight. container including means for. lvaryingathe volumeof .the. second gas-tight contaiuera and an outgassed liquid completely filling the first gastight container and the second gas-tight container, said outgassed liquid being in intimate contact with the electrical driving element and the electrical reproducer.

2. In a delay line, a first gas-tight container, an electrical driving element mounted in said first gas-tight container, an electrical reproducer mounted in said first gastight container in spaced relation to said driving element, a port in said first gas-tight container, a second gas-tight container connected to said port forming a gas-tight connection, said second gas-tight container including means for varying the volume of the second gas-tight container, and a liquid filling the first gas-tight container and the second gas-tight container, said liquid being in intimate contact with the electrical driving element and the electrical reproducer.

3. In a delay line, a first gas-tight container, an electrical driving element mounted in said first gas-tight container, an electrical reproducer mounted in said first gastight container in spaced relation to said driving element, a port in said first gas-tight container, a second gas-tight container connected to said port forming a gas-tight connection, said second gas-tight container having a member including a movable portion for varying the volume of said second gas-tight container, a liquid filling the first gas-tight container and the second gas-tight container, said liquid being in intimate contact with the driving element and the electrical reproducer, and means connected to said member for moving said movable portion in a desired direction.

4. In a delay line, a first gas-tight container, an electrical driving element mounted in said first gas-tight container, an electrical reproducer mounted in said first gastight container in spaced relation to said driving element, a port in said first gas-tight container, a second gas-tight container connected to said port forming a gas-tight connection, said second gas-tight container including a movable wall for varying the volume of said second gas-tight container, a liquid filling the first gas-tight container and the second gas-tight container, said liquid being in intimate contact with the driving element and the reproducer, and means connected to said movable wall for varying the position thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,015,063 Bennett Sept. 24, 1935 2,016,247 Simmons Oct. 1, 1935 2,025,670 Pettee Dec. 24, 1935 2,263,902 Percival Nov. 25, 1941 2,408,816 Shapiro Oct. 8, 1946 2,423,306 Forbes July 1, 1947 2,430,013 Hansell Nov. 4, 1947 2,446,835 Keary Aug. 10, 1948 2,490,452 Mason Dec. 6, 1949 2,512,156 Hofimann June 20, 1950 2,520,170 Ransom Aug. 29, 1950 2,587,304 Fiske et al Feb. 26, 1952 2,626,992 Holman Jan. 27, 1953 2,629,827 Eckert et a1. Feb. 24, 1953 FOREIGN PATENTS 227,788 Great Britain Jan. 1, 1926 

